The present invention relates to a switch and, more particularly, to a photo-switch adapted to open and close the path of photo-transmission making use of photo-transmissive bodies such as optic fibers.
Such a photo-switch has been known as having, for example, a first photo-transmissive body such as an optic fiber, a light-emitting diode provided at one end of the first photo-transmissive body to act as a light source, a second photo-transmissive body such as an optic fiber, a photo-diode as a light-receiving element and a switch circuit using a relay or the like provided at one end of the second photo-transmissive body, a switch case remote from the light source and the switch circuit and connected to the other ends of the first and second photo-transmissive bodies, and a light shielding member disposed in the switch case and adapted to selectively interrupt the transmission of light from the first photo-transmissive body to the second photo-transmissive body so as to turn on and off the light-receiving element such as a photo-diode, thereby to actuate the switch circuit by means of the output signal from the photo-diode.
This type of photo-switch is disclosed, for example, in Japanese Utility Model Laid-open No. 42259/1980.
As will be seen from FIG. 1, this known photo-switch has a tube 4 interconnecting the ends of the first and second photo-transmissive bodies 2 and 3 opposed to each other in the switch case 1. The tube 4 is adapted to be collapsed and released by the end of a light-shielding plate 6 which is rocked by the operation of a handle to selectively interrupt the light. In this known structure, therefore, it is necessary to maintain as large a distance as possible between the two photo-transmissive bodies, in order to reduce the secular change of elasticity of the tube 4 due to repeated operation. The increased distance between the two photo-transmissive bodies causes a large loss of light when the light is transmitted from the first photo-transmissive member 2 to the second photo-transmissive member 3.
It is also to be pointed out that, since the tube 4 is pressed at the same portion thereof for a number of times, the deterioration of the tube 4 is heavy to cause malfunctions.
Another known photo-switch is shown in Japanese Utility Model Laid-open No. 50550/1980. In this known photo-switch, as shown in FIG. 2, a reflecting member 8 is mounted on a movable member 7 adapted to rotate in a seesaw-like manner in the switch case 1, so as to selectively reflect the incoming light from the first photo-transmissive body 2 to selectively transmit the light to the second photo-transmissive body 3.
In this known photo-switch shown in FIG. 2, the rotary member 7 rotates along an arcuate path at a position adjacent to the ends of the first and second photo-transmissive bodies which are introduced and arranged in the switch case 1 in parallel with each other. It is, therefore, necessary to provide a required distance between the photo-transmissive bodies 2,3 and the reflecting member 8. This in turn inevitably causes a loss of light (large attenuation of light) when the switch is in the on state. In addition, due to the reflection across a predetermined space, the light from the first photo-transmissive body 2 is inevitably scattered to the region other than the second photo-transmissive body 3.
It is also to be pointed out that, since no light shielding plate is provided, there is a slight leak of light from the first photo-transmissive body 2 to the second photo-transmissive body 3 in the off state of the switch. This leak of light may cause an erroneous operation of the switch.
Another problem of the photo-switch shown in FIG. 2 is that the reflecting efficiency of the reflecting member may be drastically lowered due to dewing and clouding of the reflecting surface due to a change in the ambient temperature. The dew on the reflecting surface causes a random reflection. In order to avoid the clouding of the reflecting surface, it has been proposed to apply silicon or the like to the surface of the reflecting member. This countermeasure, however, cannot prevent condensing of dew onto the lower part of the reflecting surface.
Thus, there are many problems in the prior art.